The present invention relates in general to mobile wireless communication systems, and more particularly, to a scanning procedure for an EDGE Compact system.
Enhanced Data Rates for Global Evolution (EDGE) is an evolution of the Global System for Mobile Communications (GSM) standard and the Telecommunications Industry Association (TIA)/Electronic Industry Association (EIA) standard TIA/EIA-136 for Time Division Multiple Access (TDMA) systems that allows high rate packet data capability. There are two modes in which EDGE can be deployed, EDGE Classic, which is similar to the way EDGE is deployed in GSM systems, and an enhanced mode called EDGE Compact. EDGE Compact requires less than 1 MHz of spectrum for deployment while EDGE Classic requires 2.4 MHz of spectrum. In either case, when a mobile terminal is switched on, it is important for it to obtain service as soon as possible. For this to happen, the mobile terminal needs to read the broadcast information transmitted by the system, following which it can make a random access and register with the system. This process is described in the GSM specification, published by the European Telecommunications Standards Institute (ETSI), which deals with Radio Subsystem Link Control.
In EDGE Classic, carriers with broadcast and common control information, called BCCH carriers, are transmitted continuously with constant power, whereas other carriers may have power variations and power off conditions at different times. Thus, the channel selection procedure to find BCCH carriers as specified in the GSM standard requires the mobile terminal to do the following:                1. Measure power on all carriers at random times;        2. Average at least five of these measurements per carrier over a range of 3-5 seconds;        3. Choose the carriers with the highest average power as candidates to search for control channels.        
However, the channel selection procedure described in the GSM standard is not appropriate for EDGE Compact since the carriers with the broadcast information (called EDGE Compact primary carriers) do not transmit continuously or at a constant power level. Only the time slots with control information are required to be transmitted at maximum power, and the rest of the time slots can transmit with less than maximum power or may be idle. Thus, random measurements of signal strength have to be modified in order to make sure that a sufficient number of valid measurements are obtained, or new methods that do not rely on the such constant power level requirements need to be defined.